Editing Astronomy (section)

== History ==
{{Main|History of astronomy}}
{{For timeline}}
{{Further|Archaeoastronomy|List of astronomers}}

=== Pre-historic astronomy ===
[[File:Nebra solstice 2.jpg|thumb|The [[Nebra sky disc]] ({{circa|1800–1600 BCE}}), found near a possibly [[astronomical complex]], most likely depicting the Sun or full Moon, the Moon as a crescent, the [[Pleiades]] and the summer and winter solstices as strips of gold on the side of the disc,<ref name="Meller 2021">{{cite book|url=https://www.academia.edu/80363367|title=Time is power. Who makes time?: 13th Archaeological Conference of Central Germany|chapter=The Nebra Sky Disc – astronomy and time determination as a source of power|last=Meller|first=Harald|date=2021|publisher=Landesmuseum für Vorgeschichte Halle (Saale).|isbn=978-3-948618-22-3}}</ref><ref>{{cite AV media |url=https://www.youtube.com/watch?v=0dlijsmVJ9c&t=760s |title=Concepts of cosmos in the world of Stonehenge |website=British Museum |date=2022}}</ref> with the top representing the [[horizon]]<ref name=":03">{{Cite book |last1=Bohan |first1=Elise |url=https://www.worldcat.org/oclc/940282526 |title=Big History |last2=Dinwiddie |first2=Robert |last3=Challoner |first3=Jack |last4=Stuart |first4=Colin |last5=Harvey |first5=Derek |last6=Wragg-Sykes |first6=Rebecca |last7=Chrisp |first7=Peter |last8=Hubbard |first8=Ben |last9=Parker |first9=Phillip |collaboration=Writers |date=February 2016 |publisher=[[DK (publisher)|DK]] |others=Foreword by [[David Christian (historian)|David Christian]] |isbn=978-1-4654-5443-0 |edition=1st American |location=[[New York City|New York]] |page=20 |oclc=940282526}}</ref> and [[north]].]]

In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye. In some locations, early cultures assembled massive artifacts that may have had some astronomical purpose. In addition to their ceremonial uses, these [[Observatory|observatories]] could be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year.<ref name="history">{{cite book | first=George | last=Forbes | title=History of Astronomy | publisher=Plain Label Books | location=London | date=1909 | isbn=978-1-60303-159-2 | url=http://www.gutenberg.org/ebooks/8172 | access-date=7 April 2019 | archive-date=28 August 2018 | archive-url=https://web.archive.org/web/20180828185512/http://www.gutenberg.org/ebooks/8172 | url-status=live }}</ref>

===Classical astronomy===
[[File:Ct-33-planisphere.jpg|thumb|A Babylonian [[planisphere]] (7th century BCE). [[Babylonian astronomy]] made early advances in astronomy. Its use of [[sexagesimal]]s (e.g. 12, 24, 60, 360) is still being used today through having been broadly adopted for [[timekeeping]] and [[astrometry]].<ref name="x754">{{cite web | last=Gent | first=R.H. van | title=Bibliography of Babylonian Astronomy & Astrology | website=science.uu.nl project csg | url=https://webspace.science.uu.nl/~gent0113/babylon/babybibl.htm | access-date=2024-11-22}}</ref>]]
As civilizations developed, most notably in [[Egyptian astronomy|Egypt]], [[Babylonian astronomy|Mesopotamia]], [[Greek astronomy|Greece]], [[Persian astronomy|Persia]], [[Indian astronomy|India]], [[Chinese astronomy|China]], and [[Maya civilization|Central America]], astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as [[astrometry]]. From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon and the Earth in the Universe were explored philosophically.{{cn|date=March 2025}}

Mesopotamia is worldwide the place of the earliest known astronomer and poet by name: [[Enheduanna]], [[Akkadian Empire|Akkadian]] high priestess to the [[lunar deity]] [[Sin (mythology)|Nanna/Sin]] and princess, daughter of [[Sargon the Great]] ({{circa|2334}} – {{circa|2279}} BCE). She had the Moon tracked in her chambers and wrote poems about her divine Moon.<ref name="c099">{{cite magazine | last=Winkler | first=Elizabeth | title=The Struggle to Unearth the World's First Author | magazine=The New Yorker | date=2022-11-19 | url=https://www.newyorker.com/books/page-turner/the-struggle-to-unearth-the-worlds-first-author | access-date=2025-02-10}}</ref>

A particularly important early development was the beginning of mathematical and scientific astronomy, which began among [[Babylonian astronomy|the Babylonians]], who laid the foundations for the later astronomical traditions that developed in many other civilizations.<ref>{{cite journal|title=Scientific Astronomy in Antiquity|author=Aaboe, A. |journal=[[Philosophical Transactions of the Royal Society]]|volume=276|issue=1257|date=1974|pages=21–42|jstor=74272|doi=10.1098/rsta.1974.0007|bibcode = 1974RSPTA.276...21A |s2cid=122508567 }}</ref> The [[Babylonian astronomy|Babylonians]] discovered that [[lunar eclipses]] recurred in a repeating cycle known as a [[Saros cycle|saros]].<ref>{{cite web|url=http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |title=Eclipses and the Saros |publisher=NASA |access-date=28 October 2007 |archive-url=https://web.archive.org/web/20071030225501/http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |archive-date=30 October 2007 }}</ref>

Following the Babylonians, significant advances in astronomy were made in [[ancient Greece]] and the [[Hellenistic civilization|Hellenistic]] world. [[Greek astronomy]] is characterized from the start by seeking a rational, physical explanation for celestial phenomena.<ref>{{Cite book| last = Krafft| first = Fritz| date = 2009| contribution = Astronomy| editor-last = Cancik| editor-first = Hubert| editor2-last = Schneider| editor2-first = Helmuth| title = Brill's New Pauly| title-link = Brill's New Pauly}}</ref> In the 3rd century BC, [[Aristarchus of Samos]] estimated the [[Aristarchus On the Sizes and Distances|size and distance of the Moon and Sun]], and he proposed a model of the [[Solar System]] where the Earth and planets rotated around the Sun, now called the [[heliocentrism|heliocentric]] model.<ref>{{cite journal | title = Aristarchus's On the Sizes and Distances of the Sun and the Moon: Greek and Arabic Texts | journal = Archive for History of Exact Sciences | date = May 2007 | first1 = J.L. | last1 = Berrgren |first2= Nathan |last2= Sidoli | volume = 61 | issue = 3 | pages = 213–54 | doi = 10.1007/s00407-006-0118-4| s2cid = 121872685 }}</ref> In the 2nd century BC, [[Hipparchus]] discovered [[precession]], calculated the size and distance of the Moon and invented the earliest known astronomical devices such as the [[astrolabe]].<ref>{{cite web|url=http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Hipparchus.html|title=Hipparchus of Rhodes|publisher=School of Mathematics and Statistics, [[University of St Andrews]], Scotland|access-date=28 October 2007|archive-url=https://web.archive.org/web/20071023062202/http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Hipparchus.html|archive-date=23 October 2007 |url-status=live}}</ref> Hipparchus also created a comprehensive catalog of 1020 stars, and most of the [[constellation]]s of the northern hemisphere derive from Greek astronomy.<ref>{{cite book|last=Thurston|first=H.|title=Early Astronomy|url=https://books.google.com/books?id=rNpHjqxQQ9oC&pg=PA2|year=1996|publisher=Springer Science & Business Media|isbn=978-0-387-94822-5|page=2|access-date=20 June 2015|archive-date=3 February 2021|archive-url=https://web.archive.org/web/20210203012120/https://books.google.com/books?id=rNpHjqxQQ9oC&pg=PA2|url-status=live}}</ref> The [[Antikythera mechanism]] ({{circa|150}}–80 BC) was an early [[analog computer]] designed to calculate the location of the [[Sun]], [[Moon]], and [[planets]] for a given date. Technological artifacts of similar complexity did not reappear until the 14th century, when mechanical [[astronomical clock]]s appeared in Europe.<ref name=insearchoflosttime>{{cite journal|last1=Marchant|first1=Jo|title=In search of lost time|journal=Nature|volume=444|issue=7119|pages=534–38|date=2006|pmid=17136067|doi=10.1038/444534a|bibcode = 2006Natur.444..534M |doi-access=free}}</ref>

The Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the [[geocentric model]] of the Universe, or the [[Ptolemaic system]], named after [[Ptolemy]].<ref>{{cite book|last=DeWitt|first=Richard|title=Worldviews: An Introduction to the History and Philosophy of Science|date=2010|publisher=Wiley|location=Chichester, England|isbn=978-1-4051-9563-8|page=113|chapter=The Ptolemaic System}}</ref>

=== Post-classical astronomy ===
[[File:Al- Fargānī, Aḥmad ibn Muḥammad – Compilatio astronomica, 1493 – BEIC 13262685.jpg|thumb|Portrait of [[Alfraganus]] in the ''Compilatio astronomica'', 1493. [[Islamic astronomy|Islamic astronomers]] began just before the 9th century to collect and translate [[Indian astronomy|Indian]], [[Persian astronomy|Persian]] and [[Greek astronomy|Greek]] astronomical texts, adding their own astronomy and enabling later, particularly European astronomy to build on.<ref name="n063">{{cite web | last=Akerman | first=Iain | title=The language of the stars | website=WIRED Middle East | date=2023-05-17 | url=https://wired.me/culture/arab-astronomy-the-language-of-stars/ | access-date=2024-11-23}}</ref>]]

[[Astronomy in medieval Islam|Astronomy flourished in the Islamic world]] and other parts of the world. This led to the emergence of the first astronomical [[Observatory|observatories]] in the [[Muslim world]] by the early 9th century.<ref name="Kennedy-1962">{{Cite journal |last=Kennedy |first=Edward S. |date=1962 |title=Review: ''The Observatory in Islam and Its Place in the General History of the Observatory'' by Aydin Sayili |journal=[[Isis (journal)|Isis]] |volume=53 |issue=2 |pages=237–39 |doi=10.1086/349558 }}</ref><ref name="Micheau-992-3">{{Cite journal|last=Micheau|first=Françoise|editor-last=Rashed|editor-first=Roshdi|editor2-last=Morelon|editor2-first=Régis|title=The Scientific Institutions in the Medieval Near East|journal=Encyclopedia of the History of Arabic Science|volume=3|pages=992–93}}</ref><ref>{{cite book |last=Nas |first=Peter J|title=Urban Symbolism|date=1993 |publisher=Brill Academic Publishers |isbn=978-90-04-09855-8|page=350}}</ref> In 964, the [[Andromeda Galaxy]], the largest [[galaxy]] in the [[Local Group]], was described by the Persian Muslim astronomer [[Abd al-Rahman al-Sufi]] in his ''[[Book of Fixed Stars]]''.<ref name="NSOG">{{cite book |last1= Kepple |first1= George Robert |first2=Glen W. |last2=Sanner |title= The Night Sky Observer's Guide |volume= 1 |publisher= Willmann-Bell, Inc. |date= 1998 |isbn= 978-0-943396-58-3 |page=18}}</ref> The [[SN 1006]] [[supernova]], the brightest [[apparent magnitude]] stellar event in recorded history, was observed by the Egyptian Arabic astronomer [[Ali ibn Ridwan]] and [[Chinese astronomy|Chinese astronomers]] in 1006. Iranian scholar [[Al-Biruni]] observed that, contrary to [[Ptolemy]], the Sun's [[apogee]] (highest point in the heavens) was mobile, not fixed.<ref>{{cite news |last1=Covington |first1=Richard |title=Rediscovering Arabic Science |url=http://archive.aramcoworld.com/issue/200703/rediscovering.arabic.science.htm |access-date=6 March 2023 |work=[[Aramco World]] |issue=3 |volume=58 |date=2007 |archive-date=1 March 2021 |archive-url=https://web.archive.org/web/20210301151438/https://archive.aramcoworld.com/issue/200703/rediscovering.arabic.science.htm |url-status=live }}</ref> Some of the prominent Islamic (mostly Persian and Arab) astronomers who made significant contributions to the science include [[Al-Battani]], [[Thebit]], [[Abd al-Rahman al-Sufi]], [[Abu Rayhan Biruni|Biruni]], [[Abū Ishāq Ibrāhīm al-Zarqālī]], [[Al-Birjandi]], and the astronomers of the [[Maragheh observatory|Maragheh]] and [[Ulugh Beg Observatory|Samarkand]] observatories. Astronomers during that time introduced many [[List of Arabic star names|Arabic names now used for individual stars]].<ref name="short history">{{cite book|first=Arthur|last=Berry|title=A Short History of Astronomy From Earliest Times Through the 19th Century|publisher=Dover Publications, Inc.|location=New York|date=1961|isbn=978-0-486-20210-5|url-access=registration|url=https://archive.org/details/shorthistoryofas0000berr}}</ref><ref name="Cambridge history">{{cite book|editor=Hoskin, Michael|title=The Cambridge Concise History of Astronomy|publisher=Cambridge University Press|date=1999|isbn = 978-0-521-57600-0}}</ref>

It is also believed that the ruins at [[Great Zimbabwe]] and [[Timbuktu]]<ref>{{cite book|url=https://archive.org/details/royalkingdomsofg00patr|url-access=registration|page=[https://archive.org/details/royalkingdomsofg00patr/page/103 103]|title= The royal kingdoms of Ghana, Mali, and Songhay: life in medieval Africa|first=Pat|last= McKissack|author2=McKissack, Frederick|date=1995|publisher=H. Holt|isbn=978-0-8050-4259-7}}</ref> may have housed astronomical observatories.<ref>{{cite journal|url=https://www.newscientist.com/article/dn3137-eclipse-brings-claim-of-medieval-african-observatory.html|title=Eclipse brings claim of medieval African observatory|date=2002|journal=New Scientist|access-date=3 February 2010|last=Clark|first=Stuart|author2=Carrington, Damian|archive-date=30 April 2015|archive-url=https://web.archive.org/web/20150430173144/http://www.newscientist.com/article/dn3137-eclipse-brings-claim-of-medieval-african-observatory.html|url-status=live}}</ref> In [[Post-classical]] [[West Africa]], Astronomers studied the movement of stars and relation to seasons, crafting charts of the heavens as well as precise diagrams of orbits of the other planets based on complex mathematical calculations. [[Songhai Empire|Songhai]] historian [[Mahmud Kati]] documented a [[meteor shower]] in August 1583.<ref>{{Cite book|last=Hammer|first=Joshua|title=The Bad-Ass Librarians of Timbuktu And Their Race to Save the World's Most Precious Manuscripts|publisher=Simon & Schuster|year=2016|isbn=978-1-4767-7743-6|location=New York|pages=26–27}}</ref><ref>{{cite book |last=Holbrook |first=Jarita C. |url=https://books.google.com/books?id=4DJpDW6IAukC&pg=PA182 |title=African Cultural Astronomy |author2=Medupe, R. Thebe |author3=[[Johnson Urama]] |date=2008 |publisher=Springer |isbn=978-1-4020-6638-2 |access-date=19 October 2020 |archive-url=https://web.archive.org/web/20210817020340/https://books.google.com/books?id=4DJpDW6IAukC&pg=PA182 |archive-date=17 August 2021 |url-status=live}}</ref>
Europeans had previously believed that there had been no astronomical observation in [[sub-Saharan Africa]] during the pre-colonial Middle Ages, but modern discoveries show otherwise.<ref>{{cite web|url=http://www.scienceinafrica.co.za/2003/november/cosmic.htm |title=Cosmic Africa explores Africa's astronomy |access-date=3 February 2002 |publisher=Science in Africa |archive-url=https://web.archive.org/web/20031203055223/http://www.scienceinafrica.co.za/2003/november/cosmic.htm |archive-date=3 December 2003 }}</ref><ref>{{cite book|url=https://books.google.com/books?id=4DJpDW6IAukC&pg=PA180|title=African Cultural Astronomy|first=Jarita C.|last=Holbrook|author2=Medupe, R. Thebe|author3=Urama, Johnson O.|publisher=Springer|date=2008|isbn=978-1-4020-6638-2|access-date=26 August 2020|archive-date=26 August 2016|archive-url=https://web.archive.org/web/20160826084847/https://books.google.com/books?id=4DJpDW6IAukC&pg=PA180|url-status=live}}</ref><ref>{{cite web|url=http://royalsociety.org/news.asp?year=&id=4117 |title=Africans studied astronomy in medieval times|date=30 January 2006|publisher=The Royal Society|access-date=3 February 2010 |archive-url = https://web.archive.org/web/20080609112829/http://royalsociety.org/news.asp?year=&id=4117 |archive-date = 9 June 2008}}</ref><ref>Stenger, Richard {{cite news|url=http://articles.cnn.com/2002-12-05/tech/zimbabwe.observatory_1_supernova-forecast-eclipses-star |title=Star sheds light on African 'Stonehenge' |work=CNN |date=5 December 2002 |archive-url=https://web.archive.org/web/20110512162930/http://articles.cnn.com/2002-12-05/tech/zimbabwe.observatory_1_supernova-forecast-eclipses-star?_s=PM%3ATECH |archive-date=12 May 2011 }}. CNN. 5 December 2002. Retrieved on 30 December 2011.</ref>

For over six centuries (from the recovery of ancient learning during the late Middle Ages into the Enlightenment), the [[Roman Catholic Church]] gave more financial and social support to the study of astronomy than probably all other institutions. Among the Church's motives was finding the [[Date of Easter|date for Easter]].<ref>J.L. Heilbron, ''The Sun in the Church: Cathedrals as Solar Observatories'' (1999), p. 3</ref>

Medieval Europe housed a number of important astronomers. [[Richard of Wallingford]] (1292–1336) made major contributions to astronomy and [[horology]], including the invention of the first astronomical clock, the [[Rectangulus]] which allowed for the measurement of angles between planets and other astronomical bodies, as well as an [[equatorium]] called the ''Albion'' which could be used for astronomical calculations such as [[moon|lunar]], [[sun|solar]] and [[planet]]ary [[longitude]]s and could predict [[eclipse]]s. [[Nicole Oresme]] (1320–1382) and [[Jean Buridan]] (1300–1361) first discussed evidence for the rotation of the Earth, furthermore, Buridan also developed the theory of impetus (predecessor of the modern scientific theory of [[inertia]]) which was able to show planets were capable of motion without the intervention of angels.<ref>Hannam, James. ''God's philosophers: how the medieval world laid the foundations of modern science''. Icon Books Ltd, 2009, 180</ref> [[Georg von Peuerbach]] (1423–1461) and [[Regiomontanus]] (1436–1476) helped make astronomical progress instrumental to Copernicus's development of the heliocentric model decades later.{{cn|date=March 2025}}

=== Early telescopic astronomy ===
[[File:Galileo's sketches of the moon.png|thumb |upright |The first sketches of the Moon's topography, from [[Galileo]]'s ground-breaking ''[[Sidereus Nuncius]]'' (1610), publishing his findings from the first telescopic astronomical observations.]]

During the [[Renaissance]], [[Nicolaus Copernicus]] proposed a heliocentric model of the solar system. His work was defended by [[Galileo Galilei]] and expanded upon by [[Johannes Kepler]]. Kepler was the first to devise a system that correctly described the details of the motion of the planets around the Sun. However, Kepler did not succeed in formulating a theory behind the laws he wrote down.<ref>{{harvnb|Forbes|1909|pp=49–58}}</ref> It was [[Isaac Newton]], with his invention of [[celestial dynamics]] and his [[gravity|law of gravitation]], who finally explained the motions of the planets. Newton also developed the [[reflecting telescope]].<ref name="f58-64">{{harvnb|Forbes|1909|pp=58–64}}</ref>

Improvements in the size and quality of the telescope led to further discoveries. The English astronomer [[John Flamsteed]] catalogued over 3000 stars.<ref>Chambers, Robert (1864) ''[[Chambers Book of Days]]''</ref> More extensive star catalogues were produced by [[Nicolas Louis de Lacaille]]. The astronomer [[William Herschel]] made a detailed catalog of nebulosity and clusters, and in 1781 discovered the planet [[Uranus]], the first new planet found.<ref>{{harvnb|Forbes|1909|pp=79–81}}</ref>

During the 18–19th centuries, the study of the [[three-body problem]] by [[Leonhard Euler]], [[Alexis Claude Clairaut]], and [[Jean le Rond d'Alembert]] led to more accurate predictions about the motions of the Moon and planets. This work was further refined by [[Joseph-Louis Lagrange]] and [[Pierre Simon Laplace]], allowing the masses of the planets and moons to be estimated from their perturbations.<ref>{{harvnb|Forbes|1909|pp=74–76}}</ref>

Significant advances in astronomy came about with the introduction of new technology, including the [[spectroscope]] and [[Astrophotography|photography]]. [[Joseph von Fraunhofer]] discovered about 600 bands in the spectrum of the Sun in 1814–15, which, in 1859, [[Gustav Kirchhoff]] ascribed to the presence of different elements. Stars were proven to be similar to the Earth's own Sun, but with a wide range of [[temperature]]s, [[mass]]es, and sizes.<ref name="short history" />

=== Deep space astronomy ===
[[File:Andromeda_Nebula_-_Isaac_Roberts,_29_December_1888 (cropped).jpg|thumb|The earliest known photograph of the [[Andromeda Galaxy|Great Andromeda "Nebula"]], by [[Isaac Roberts]] from 29 December 1888. With the calculation of its distance in 1923 [[intergalactic space]] was proven, allowing the calculation of the age and expanse of the [[Universe]].]]
The existence of the Earth's galaxy, the [[Milky Way]], as its own group of stars was only proven in the 20th century, along with the existence of "external" galaxies. The observed recession of those galaxies led to the discovery of the expansion of the [[Universe]].<ref name=Belkora2003>{{cite book|author=Belkora, Leila|title=Minding the heavens: the story of our discovery of the Milky Way|isbn=978-0-7503-0730-7|url=https://books.google.com/books?id=qBM-wez94WwC|publisher=[[CRC Press]]|date=2003|pages=1–14|access-date=26 August 2020|archive-date=27 October 2020|archive-url=https://web.archive.org/web/20201027093857/https://books.google.com/books?id=qBM-wez94WwC|url-status=live}}</ref> In 1919, when the [[Hooker Telescope]] was completed, the prevailing view was that the universe consisted entirely of the Milky Way Galaxy. Using the Hooker Telescope, [[Edwin Hubble]] identified [[Cepheid variable]]s in several spiral nebulae and in 1922–1923 proved conclusively that [[Andromeda Galaxy|Andromeda Nebula]] and [[Triangulum Nebula|Triangulum]] among others, were entire galaxies outside our own, thus proving that the universe consists of a multitude of galaxies.<ref name="SharovNovikov1993">{{cite book|last1=Sharov|first1=Aleksandr Sergeevich|last2=Novikov|first2=Igor Dmitrievich|title=Edwin Hubble, the discoverer of the big bang universe|url=https://books.google.com/books?id=ttEwkEdPc70C&pg=PA34|access-date=December 31, 2011|date=1993|publisher=Cambridge University Press|isbn=978-0-521-41617-7|page=34|archive-date=June 23, 2013|archive-url=https://web.archive.org/web/20130623075250/http://books.google.com/books?id=ttEwkEdPc70C&pg=PA34|url-status=live}}</ref> With this Hubble formulated the [[Hubble constant]], which allowed for the first time a calculation of the age of the Universe and size of the Observable Universe, which became increasingly precise with better meassurements, starting at 2 billion years and 280 million light-years, until 2006 when data of the [[Hubble Space Telescope]] allowed a very accurate calculation of the age of the Universe and size of the Observable Universe.<ref name="p537">{{cite web | title=Cosmic Times | website=Imagine the Universe! | date=December 8, 2017 | url=https://imagine.gsfc.nasa.gov/educators/programs/cosmictimes/educators/guide/age_size.html | access-date=October 31, 2024}}</ref>

[[File:Black hole - Messier 87 crop max res.jpg|thumb|First ever direct image of a ([[supermassive black hole|supermassive]]) [[black hole]], taken 2019 [[Radio astronomy|in radio wavelength]], located at the core of [[Messier 87]].]]

Theoretical astronomy led to speculations on the existence of objects such as [[black hole]]s and [[neutron star]]s, which have been used to explain such observed phenomena as [[quasar]]s, [[pulsar]]s, [[blazar]]s, and [[radio galaxy|radio galaxies]]. [[Physical cosmology]] made huge advances during the 20th century. In the early 1900s the model of the [[Big Bang]] theory was formulated, heavily evidenced by [[cosmic microwave background radiation]], [[Hubble's law]], and the [[Big Bang nucleosynthesis|cosmological abundances of elements]]. [[Space telescope]]s have enabled measurements in parts of the electromagnetic spectrum normally blocked or blurred by the atmosphere.<ref>{{cite book | chapter=Beating the atmosphere | first=Ian S. | last=McLean | title=Electronic Imaging in Astronomy | series=Springer Praxis Books | date=2008 | isbn=978-3-540-76582-0 | pages=39–75 | publisher=Springer | location=Berlin, Heidelberg | doi=10.1007/978-3-540-76583-7_2 }}</ref> In February 2016, it was revealed that the [[LIGO]] project had [[first observation of gravitational waves|detected evidence]] of [[gravitational waves]] in the previous September.<ref name="Discovery 2016">{{cite journal |title=Einstein's gravitational waves found at last |journal=Nature News |url=http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361 |date=11 February 2016 |last1=Castelvecchi |first1=Davide |last2=Witze |first2=Witze |doi=10.1038/nature.2016.19361 |s2cid=182916902 |access-date=11 February 2016 |archive-date=12 February 2016 |archive-url=https://web.archive.org/web/20160212082216/http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361 |url-status=live }}</ref><ref name='Abbot'>{{cite journal |title=Observation of Gravitational Waves from a Binary Black Hole Merger| author=B.P. Abbott |collaboration=LIGO Scientific Collaboration and Virgo Collaboration| journal=Physical Review Letters| year=2016| volume=116|issue=6| pages=061102| doi=10.1103/PhysRevLett.116.061102| pmid=26918975| bibcode=2016PhRvL.116f1102A|arxiv = 1602.03837 | s2cid=124959784}}</ref>